High-compression motor fuels and their manufacture



Patented Jan. 13, 1948 HIGH-COMPRESSION MOTOR FUELS AND THEIRMANUFACTURE Pha-ris Miller, Elizabeth, N. J., assignor to Standard OilDevelopment Company, a corporation of Delaware N Drawing. ApplicationMarch 27, 1941, Serial No. 385,496

This invention relates to high-compression.

motor fuels constituted to be knock-free in road performance and totheir manufacture.

Gasoline-type fuels of improved anti-knock qualities are needed ingreater volume for highpowered motors being increasingly used, yet theprincipal fuel manufacturing processes continue to yield motor fuelswhich do not give knock-free performance in thes motors at all speedswith practical additions of anti-knock agents, such as tetraethyl lead.An object of this invention is to provide fuels which give uniformlyknock-free road performance in motors having compression ratios above6.5:1 with a minimum of processing and economy in the use of theanti-knock addition agents.

In order to make the advantages of this invention more clearlyunderstood, it is considered desirable to briefly discuss differencesbetween methods used in rating the anti-knock value of motor fuels andthe significance of these metheds.

The anti-knock rating of a motor fuel is basically obtained by directcomparison of the knock intensity it produces with that produced by astandard fuel, i. e., a fuel consisting of normal heptane and iso-octane(2,2,4-trimethylpentane).

In the standardized laboratory test developed by the Cooperative FuelResearch Committee, a C. F. R. engine operated at 600 R. P. M. at roomtemperature is used in testing the fuel, and the fuel is determined tohave an octane number in terms of the per cent by volume of iso-octanein the standard fuel which matches the knock intensity of the fuel beingrated.

More recently the described laboratory method, known as the researchmethod, was modified to what is called the C. F. R. motor method,because results of the research method do not cor relat with serviceresults. The C. F. R. motor method differs from the earlier procedure inthat the engine is operated at 900 R. P. M. instead of 600 R. P. M., themixture temperature is at 300 F. instead of room temperature, and thespark timing is advanced 3.5".

To determine actual service performance of motor fuels, a road ratingmethod has been developed. The road rating differs from the laboratoryratings in that the test engines are run at various speeds, aremulticylinder, are subjected to variations in spark timing, and by otherfactors, such as fuel mixture distribution. Just as there arediscrepancies between the motor method and the research method ratings,there 2 Claims. (01. 196-50) are discrepancies between these laboratoryratlugs and the road ratings for fuels. The difference between theresearch method and the motor method ratings has been called thesensitivity of a fuel, which is somewhat a measure of relativesusceptibility of a fuel to changes in operating conditions, and fuelswith the greatest sensitivity, in general, show the greatest increase orappreciation to higher road ratings.

Motor fuel compositions for spark-ignition engines with high-compressionratios are efificiently modified in accordance with the presentinvention to have satisfactorily improved road octane ratings andresponsiveness to anti-knock addition agents so that they giveknock-free performance at all speeds. This improvement is important forsecuring greater thermodynamic efficiency in the operation of thehigh-compression motors.

At present, commercial gasolines of highest anti-knock quality aremanufactured principally by cracking, reforming, gas polymerization, andalkylation processes. Some of these gasolines contain substantialproportions of olefins ranging from 5% to 50% or higher, but the olefinstherein, if present in any such substantial amounts, are distributedthroughout the boiling range of the fuel and volatilize mostly with themajor portion of the fuel boiling above 158 F.

There are considerable differences between the road performances ofcommercial gasolines obtained by these variou processes. In one respector another, they have not given satisfactory knock-free performance withpracticable additions of anti-knock agents when used in modernhigh-powered motors.

In accordance with the present invention, gasoline products are improvedin appreciation for securing knock-free road performance at both low andhigh speeds by a treatment which radically modifies the fuelcompositions, so that the fuels contain a certain high concentration oflow boiling olefins in the fraction distilling off below 158 F., and aminimum content of the higher olefin or non-benzenoid unsaturatedhydrocarbon components boiling above 158 R, such higher olefins beingeliminated to the extent that the volume ratio of said low boilingolefins to said higher olefins is preferably less than 9:1, without asubstantial change in the desired volatility or boiling characteristicsof the fuel and without detrimental effects on the vapor pressure.

In carrying out the present invention, first it Q is desirableto preparegasoline base stocks of suitable boilin range, volatility, and good in-3 herent anti-knock quality, 1. e., having boiling ranges within thelimits of 75 F. and 450 F., more preferably between 100 F. and about 300F. or 400 F. with mid-boiling points above 1 58" F., preferably between200 and 250 F., and inherent A. S. T. M. octane ratings of 70 or better,and to form and treat the fuels in such a manner, that upon analysis,the finished fuel shows a total olefin content of from at least 10% to50% and. preferably about 12% to 30% by volume, with the olefinsconcentrated principally in the front volatile portion of the fuel to anextent that most of the total olefin content, preferably more than 90%thereof, boils off with the portion distilled off up to 158 F. andconstitutes the bulk of this portion.

In the interest of economical processing, the hydrocarbon components ofthe fuel other than the olefins, in general, comprise paraffinic,isoaraffinic, naphthenic, aromatic, or mixed hydrocarbon compounds ofthese types, as they result from various refining and conversionprocesses applied to petroleum oils in making commercial gasoline fuelproducts.

The present procedure is valuable in treating mixed gasoline fuel stockswhich separately or blended in a conventional manner do not havesuitable road octane ratings for use in high-compression motors.However, the present procedure is very useful in processing a singlefuel stock; for example, if it is desired to modify a cracked gasoline,the cracked gasoline is subjected to operations designed to enrich theolefin content of the fuel in the portion boiling below 158 F. and toreduce the olefin content of the fuel fraction boiling above 158 F. to aminimum without detracting from the boiling characteristics of the fuelso that the'finished fuel has the desired overall content of olefins,principally concentrated in the front end portion.

The gasoline to be modified may be'obtained by vapor phase cracking ofgas oil or by polymerization of normally gaseous olefins, thermal orcatalytic, under conditions to form a large amount of olefins in thefuel. The low boiling olefins may be concentrated by fractionaldistillation or selective solvent treatment to supply the desired frontend composition of the improved fuels. As needed, low boilinghydrocarbon fractions, rich in these low boiling olefins, are obtainableby dehydrogenating processes to fill in the front ends of the modifiedfuels.

In treating the gasoline stocks for the purpose of eliminating olefinsfrom the fractions boiling above 158 R, such higher boiling fractionsmay be treated by hydrogenation or polymerization properly controlled toreduce olefinicity while keeping the distillation characteristicssubstan- If the sulfur content of. the resulting. fuelv prodnot is toovhigh, either. for the reason that the sulfur content in the initialmaterial is too h gh or due to insufficient removal of the sulfur duringthe processing, suitable additional treatment may be given to reduce thesulfur content to below 0.1% or still lower without affecting the 4hydrocarbon composition. The reduction of the sulfur content may beaccomplished by known methods such as soda washing or sweetening.

In the treatment of the fuel for the purpose of 5 the present invention,the non-benzenoid unsaturated hydrocarbons having undesirable gumformingtendencies, such as particularly diolefins, cyclic olefins, andtriolefins will be effectively removed from the higher boiling portionsof the fuel, and such unsaturates are readily reduced to a negligibleamount of less than 1% in the low boiling portions of the fuel by anadsorptive clay treatment or other established refining methods withoutsubstantially diminishing the desired high concentration ofmono-olefins. However, the presence of certain low molecular weightdiolefins containing only 4 to 6 carbon atoms per molecule, particularlysuch as butadiene or methyl-butadiene, may be permitted to remain in thefront ends without serious impairment to the stability of the fuel inthe presence of a gum inhibitor, since such low boiling diolefins aresufficiently stable, provided higher diolefins are absent, to preventany marked deterioration of the fuel over a normal storage period with asmall amount of inhibitor present. Nevertheless, it is intended to havepreferably the more common and more stable mono-olefins or alkenes asthe olefinic constituents of the improved fuel.

It might be noted that whereas in conventional refining practice anover-all reduction of olefin content is frequently made, or the olefincontent of the fuel is particularly reduced in the front ends byrefining or in special processing, such as by alkylation orpolymerization, the present invention quite differently provides forsubstantially raising the concentration of the low boiling olefins whileeliminating the higher boiling olefins and reducing the content of lowboiling saturates.

As illustrative of the invention, the following examples are given:

Example An East Texas gas oil, when subjected to intensifieddehydrogenation conditions in catalytic cracking is made to form agasoline product having an exceptionally high olefin content.Satisfactory conditions used in this operation are summarized asfollows:

Activated clay, silica-alumina gels,

Type of Catalyst silica-magnesia gels e, Secs Yield, Based on Output,Vol. percent Gasoline products obtained by the described crackingoperation have the following compositions:

Volume, Components percent 5 Total Olefins 58-74 Aromatics 9- 5Naphthenes 12-11 Paraflins', normal and branched.....- 21-40 olefinsDistilled Off Below 158 F. (Percentage of Total 5-12 Oleflns) By varyingthe conditions in the catalytic cracking operation, the olefin contentand the olefin concentration in the front ends are varied to somedegree, but nevertheless the resulting fuel product contains aconsiderable excess of higher boiling olefins which distill off atabove158 F.

A gasoline product resulting from cracking processes with intensifieddehydrogenation, as described, contains large amounts of olefins, henceit can be fractionated to separate the front end fraction boiling belowabout 158 F. and a fraction boiling from about 158 F. to about 350 or400 F., thus furnishing a gasoline which is well adapted for processingin accordance with the present invention. The front end fraction may beenriched in C4, C5, and C6 olefins in proper amounts, with decrease incorresponding amounts of analogous paraflins to obtain suitablevolatility characteristics depending upon the needs of the fuel. Thisincrease in the concentration of any of these particular olefins iseasily made without giving the fuel an excessive vapor pressure bysimply making sharp cuts above the initial point of the front ends wheredesired and adding the desired low boiling olefins to replace lowboiling saturated hydrocarbons eliminated in making the cut. I

The separated higher boiling fraction of the cracked gasoline, which isout between about 158 g F. to about 350 or 400 R, when subjected to ahydrogenation treatment under controlled conditions to avoid substantialchange in boiling characteristics undergoes a reduction in olefincontent to a very low amount, and the conditions can be made such thatthe olefin content is reduced to well below and preferably to below 5%.Then upon recombining the thus treated fraction boiling above 158 F. oflowered olefin content and the thus treated front end fraction boilingbelow 158 F., enriched in olefins, the resulting modified fuelcomposition has in every respect desired physical characteristics ofvolatility and distillation with a considerable improvement in the roadoctane rating over the initial gaso line product which was treated as isdenoted in the following data.

A very effective method for eliminating olefins from the gasolinefraction boiling above 158 F. is one in which this fraction is subjectedin vapor phase to a catalyst that selectively promotes hydrogenation ofthe olefins with a limited amount of cracking so as to avoid changes inthe boiling characteristics of the fraction treated. There may be inthis treatment some rearrangement or combination of the molecules, butthe main effect is the reduction in olefin content to less than 10% andas low as about 1%. Satisfactory conditions for this type of operationare summarized as follows:

Activated alumina or magnesia impregnated with 1 to 50% by weight of asulfide or oxide of metals in Groups 4, 5, and 8 ol the Periodic Table;preferably with oxides of chromium Type of Catalyst The resultingmodified gasoline obtained by the described treatment for reduction ofolefins boiling within the range of about 158 F. and 400 F.

and increase in the proportion of lower boiling olefins hassubstantially the same distillation characteristics as the initialgasoline treated, as illustrated in the following table:

Initial Gasoline From Oaialyt- Modified ically Cracked Gasoline Gas OilGravity, A. P. I 59. 8 52.6 Reid Vapor Pressure (lbs/sq. in.) 8. 0 7. 0A. S. T. M. Distillation Per cent Distilled at F.:

158 14. 5 13. 0 2l2 46. 0 45.0 257 75. 0 76. 0 266 80. 0 81. 5 302-- 93.5 95.0 Final Boiling Point 333 318 Total Olefin Content, Vol. Per cent".50 13 Olefins Boiling Above 158 F., Vol.

Per cent 40 1 Olefins Boiling Below l58 F., Vol.

Per cent 10 12 Anti-knock rating tests were made on the ini- I tialgasolines and the modified gasolines, separately and blended, and withan addition of 2.75 cc. of tetraethyl lead (T. E. L.) per gallon. Theinitial gasoline products from the catalytically cracked gas oil showeda definite tendency to knock in a 73:1 compression-ratio Chryslerautomobile engine at high speeds (35 to 60 miles per hour). A roadrating test with the same type of engine run on a gasoline formed by thedescribed hydrogenation treatment so that the gasoline had a totalolefin content of less than 10% by volume showed that this type of fuelof extremely low total olefin content has a tendency to knock in thesame type of high-compression engine at low speeds (10 to 35 miles perhour). The modified gasoline containing more than 10% by volume ofolefins but with at least of these olefins concentrated in the frontends which distill off below 158 F. gave entirely knock-free performancein the same-type of high-compression engine at both the low and highspeeds.

Road Octane Ratings With 2.75 cc. T. E. LJGal.

10-35 Miles 35-60 Miles Per Hour Per Hour Initial Cracked Gasoline. 93.0 S7. 8 Hydrogenated Gasolina. 86.3 90.0 Modified Gasoline 93. 7 93. 7

The marked improvement in the gasoline cannot be accounted for by thereduction in total olefin content but is indicated to be dependent onthe modification treatment, whereby the olefins are present in asubstantial proportion of at least 10% but are concentrated in the frontends distilling off below 158 F.

A further illustration of how the road octane ratings of the motor fuelsare improved by increasing theproportion of the low boiling olefins isdemonstrated in a series of tests on a variety of modified gasolinesamples from catalytlcally nearly the same total olefin content weretested for anti-knock value to obtain the following data:

- Road Rating Average Total Octane Ratmg Car At 70 F. Olefin Content,

Volgme l gr. R Cl +1 5% Per out or osearc ear Method Method TEL/Gd- I 1-49 79. 7 90. 9 87 90 II 46 79. 7 92. 1 89 91' It is important to notethat it is not the total olefin content which is the determining factorof appreciation toward improved road rating, but more particularly theconcentration of the low boiling olefins having from 4 to 6 carbon atomsper molecule.

As hereinbefore described, highly desirable gasoline fuels of improvedroad octane rating are prepared from mixtures of hydrocarbons havingnormal gasoline distillation characteristics, i. e., preferably withinitial and final boiling points between 100 F. and 400 F., with amid-boiling point preferably no lower than about 200 F., and so modifiedas to contain preferably from 10 to 50% of olefins, with a minimum ofmono-olefins boiling above 158 F., so that at least 90% of the olefinsare in the front ends boiling below 153 F.

The herein described modification of gasolines is subject to certainvariations depending upon the grade and purpose needed. For summer gradefuels, the modified gasoline preferably should have less than 20%distill off at 158 and contain from 10% to 20% of C and C6 olefins. Fora, winter grade, the modified gasoline may contain from 20 to 30% of C4to C6 olefins, which distill off below 158 F. Also, aviation fuels maybe prepared in accordance with the present invention, because themodified fuels contain relatively low total amounts of olefins, havesuitably low Reid vapor pressures, and yet have suitable boiling ranges.The modified fuels, in general, have'normal Reid vapor pressures in therange of 5 to about 15 pounds per square inch at 100 F., and moreparticularly between '7 to 12 lbs. per square inch at 100 F., becausethe C. to Ca olefins are present in balanced concentrations with anextremely low amount of other hydrocarbons in the same distillationrange. By having the combined C4 to C6 olefins constitute the major partof the front ends boiling below 158 F., with lowering of the C4 to C6alkanes in these front ends in an amount corresponding to the enrichmentby the analogous low boiling alkenes and the described treatment of thehigher boiling portion of the fuel, the vapor pressure is properlymaintained and even somewhat lowered despite an increase in the volumeof the front end fraction. The mixture of C4 to Csalkenes, in general,will be made to constitute at least 75% and preferably more than 90% ofthe front ends boiling below 158 F.

The improved gasolines may contain metalloorganic anti-knock agentsother than tetraethyl lead, or other additives, such as a top cylinderlubricant, a gum-fiuxing agent, thickening agents, dyes, gum inhibitors,such as amino and phenolic compounds, or anti-knock blending agents,such as alcohols, branched ethers, or others of this type of agent,corrosion inhibitors, etc.

The foregoing examples are illustrative of the invention, andmodifications may be made which come within the spirit of the inventionas recited in the appended claims.

I claim:

1. The method of preparing a motor fuel with improved road octane ratingand lead susceptibility, which comprises treating a cracked gasoline ofhigh olefin content and containing substantial amounts of aromatic andnaphthenic hydrocarbons to replace paraffinic components of a gasolinefraction boiling below 158 F. by monoolefins having 4 to 6 carbon atomsper molecule until said monoolefins constitute at least by volume ofsaid fraction and from 10 to 30% by volume of the fuel, hydrogenatingthe fraction of said gasoline boiling above 158 F. with hydrogen in thepresence of a catalyst under suitable conditions to reduce the olefincontent thereof to less than 10% by volume while maintaining thedistillation characteristics substantially unaltered, and recombiningthe olefin-enriched fraction boiling below 158 F. with the hydrogenatedfraction boiling above 158 F.

2. The method of preparing a knock-free inotor fuel for spark ignitionengines having compression ratios above 6511 from a cracked gasolinemixture of hydrocarbons having a high con.- tent of olefins andcontaining a substantial amount of aromatic and naphthenic hydrocarbons,the major part of which boil above 158 R, which comprises replacing saidolefins boiling above 158 F. by hydrogenated derivatives thereof toreduce the olefin content of the hydrocarbons boiling above 158 F. toless than 10% by volume, and concentrating olefins having 1 to 2 doublebonds and 4 to 6 carbon atoms per molecule in the fraction of thegasoline distilling below 158 F. so that the gasoline contains from 10%to 50% by volume of non-benzenoid unsaturates with at least about byvolume of the total volume of olefins in the fraction of the fueldistilling below 158 F. while maintaining the distillationcharacteristics of the gasoline so that it has a mid-boiling point inthe range of 200 F. to 250 F. and a boiling range within the approximatelimits of F. to 400 F.

PHARIS' MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Nash et al., Principles of MotorFuel Preparation and Application, vol. II (1935, John Wiley) pages341-346.

